My b2evolution Version: 2.x

Hi,
I want to move all my posts from 5 differents blogs to only 1 main blog.
If I click on "new category", I get a icon to move root category to another blog (my advanced config about cross posting is set to 3).
But I get this error :

Notice: Trying to get property of non-object in C:\internet\wamp\www\b2evo\inc\chapters\views\_chapter_move.form.php on line 55
Nom:

Fatal error: Call to a member function get_Blog() on a non-object in C:\internet\wamp\www\b2evo\inc\chapters\views\_chapter_move.form.php on line 58

Is there another way to solve/do it?
Thanks,
Mel
PS I don't care if in process I loose categories, I just want to keep those posts in a new unique category. If in process, I'm get ride of all my empty category I will be happy.